What is an Unvented Cylinder?

If you’re having your heating and hot water system replaced or upgraded, the engineer might discuss options when it comes to your hot water cylinder. There are two types of stored hot water cylinders  – vented (also known as open vented or gravity fed), and unvented.

A vented cylinder  has a vent pipe that allows for expansion in the system,  it is fed from a cold water cistern tank that’s usually located in the loft. Gravity  pulls water from the tank to  the vented cylinder.

In contrast, an unvented cylinder is fed directly from the cold mains supply, meaning that there is no need for a tank in the loft space. Thanks to the direct feed from the cold mains supply, unvented cylinder systems benefit from improved pressure and flow rate.

Is an Unvented Cylinder Right For my Home?

Unvented cylinder hot water systems are typically more expensive to install than open vented systems, and if the cold water mains supply is cut off, you’ll have to go without hot water for a short while. However, there are multiple advantages to having an unvented cylinder in your home:

• They provide higher water pressure than a vented system, so the water coming out of your taps and showers is higher than a gravity fed system. This is particularly useful if you have multiple bathrooms which might have several taps running at once
• There is no requirement for a water tank, freeing up space and offering more flexibility on where it can be fitted – great for smaller homes
• Because it doesn’t rely on gravity to feed the boiler, an unvented cylinder system can be fitted practically anywhere in the home
• They’re also much quieter; vented systems with water tanks require constant refilling which can be noisy, unvented systems are much less noisy in comparison
• You don’t have to worry about the water tank freezing throughout the winter
• An unvented system is completely sealed, so the water isn’t at risk of contamination from foreign materials making their way into the tank. This also minimises the risk of damage

How Does an Unvented Cylinder Work?

Unvented hot water systems all function in roughly the same manner:

1. Cold water from the mains supply fills the cylinder
2. Hot water from the central heating system or boiler travels through the cylinder via a coil, which heats the cold water
3. The cylinder distributes hot water to taps or showers as and when required
4. As some hot water gets released, the cylinder once again fills up with cold water from the mains
5. The cycle continues on demand.

Unvented hot water systems are incredibly complex, and operate under extreme pressure, so you should never attempt to install one yourself. Only qualified installers are legally allowed to install these systems, so you should always contact a trained and qualified engineer, like our Metro Plumb experts who are available 24/7/365 for boiler and heating system enquiries.

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